In fuel cell power plants using reformate gas, it is necessary to remove carbon monoxide from the reformate gas generated by a reformer. In JP2000-169106 published by the Japanese Patent office in 2000, a carbon monoxide oxidizer is disclosed. The carbon monoxide oxidizer comprises two preferential oxidation reactors (PROX reactors) which are arranged in series. A catalyst comprising a noble metal is disposed inside the preferential oxidation reactors. Air is respectively supplied to the PROX reactors, and the catalyst removes CO in the reformate gas by reacting the CO in the reformate gas with oxygen (O2) in the air to produce carbon dioxide (CO2).
JP08-329969 published by the Japanese Patent Office in 1996 discloses a method where the reaction amount of the PROX reactor is controlled by increasing the air supply amount to the PROX reactor according to the increase in the CO concentration in the reformate gas.